1. Field of the Invention
The present invention relates to a fluid-mechanical drive for a press brake.
2. Description of the Prior Art
According to the conventional press brake construction of the prior art as shown in FIG. 1 of the application drawing, an upper movable, heavy steel blade 10 is moved vertically between an upper retracted position shown and a downwardly extended position for coaction with a stationary lower blade 12 by a pair of hydraulic cylinders 14, 15 connected at one end to stationary upright end frame members 16, 18 and at the other end to end portions of the upper blade. The large forces acting down on the opposite ends of the upper blade 10 require that the central vertical dimensions of such upper blade 10 be substantially greater than the same dimensions at the opposite ends of such blade to minimize blade deflection when the two blades coact against a metal workpiece (not shown) inserted between the upper and lower blades for forming. Lower blade 12 is similarly dimensioned for the same reason. Additional driving cylinders similar to end cylinders 14 and 15 cannot be used at intermediate positions along the movable blade to obviate the deflection problem because the space behind blades between end members must be kept clear of additional support framework to accomodate the workpieces to be formed.
The desirability of eliminating the massive central portion of at least the upper blade member 10 will be apparent, both from the standpoint of cost and weight saving and to better control deflection.
According to one prior suggested solution to the foregoing problem, as shown in prior U.S. Pat. No. 2,890,649, one single-acting central fluid cylinder-piston unit is carried by the upper blade at its midpoint and has an upwardly extensible piston with a pair of pivot links extending upwardly therefrom. The pivot links are pivoted to the inner ends of lever members which extend outwardly in opposite directions along the upper blade from the piston-cylinder unit. The lever members are pivoted to the front faces of upright end frame members and extend outwardly along the blade therefrom. The outer ends of the lever members are then pivotally connected by linkages to the outer ends of the upper blade. Although such a prior construction has some tendency to distribute downward driving forces along the length of the upper blade, it only partially fulfills this objective since it concentrates the applied forces at the midpoint and opposite ends of the upper blade. Furthermore, such prior construction still requires an upper blade with central blade portion of increased vertical dimension to mount the piston-cylinder unit, and a piston-cylinder unit of special construction. Such prior construction additionally requires supplementary fluid retraction cylinders to lift the upper blade to its open position since the primary piston-cylinder unit is single-acting.
Accordingly, there is still a need for a press brake drive which successfully distributes driving forces along the length of the upper blade in a manner which eliminates the need for an upper blade with an enlarged massive central blade portion and which can be accomodated to existing press brakes and their hydraulic systems.